Pregnant on implant?

Tane

I've had the implant since December 2016 and have not had a period until now. For the last 4-5 days I have had vaginal bleeding but the blood has been thick and black. I've also had sharp shooting pains in my abdomen on and off for the last week or so, along with sensitive boobs. My boyfriend and I only use the implant as contraception and he mainly finishes inside of me. Could I be pregnant?